The present invention relates to a method and arrangement for measuring the level of a fluid or other suitable substance contained in a container, as well as to a method and arrangement for controlling the level of a fluid or other suitable substance contained in a container.
Such methods and arrangements may be used in many fields concerned with the sucking-off or delivery of a fluid or other suitable substance, especially in the level measurement and/or control associated with extracorporal blood circulation.
The methods and arrangements described hereinafter are particularly suited for use in the medical field, but the principle described may also be used to advantage in other fields, notably when the level of a fluid or particulate mass contained in a natural or artificial container is to be measured and/or controlled.
In the medical field, surgical operations often require the blood to be sucked out of a wound. An example thereof is the so-called open-heart surgery. The blood is sucked out of the wound (heart) by means of a suction nozzle and is subsequently extracorporally circulated through an appropriate apparatus, during which circulation the blood may be subjected to a certain treatment, and is finally re-introduced into the body.
It is vital that no air bubbles are formed during sucking. The suction nozzle should therefore extend into a puddle of blood during the entire sucking operation. Moreover, to prevent blood damage, the sucking may not be performed at a too high acceleration. Furthermore, direct contact between electrodes and blood or tissue is often undesirable.
It is an object of the present invention to provide a method based on the concept of capacitive or inductive measurement of the conductivity of the fluid or other substance, which method solves the above problems.